Running lean when on boost.
Turbo Mini Forums

Just after Christmas we fitted a megajolt unit to the turbo mini. We have also just installed a new jet. We also fitted a new turbo back in september. The car was running very well, but to be on the safe side we wanted it tuned. So today, now that there is some spare cash, we took the car for a RR session in cheltenham.
Unfortunately the chap started setting up the fueling and noticed that the car was running way lean as soon as it came on boost. Tick over and revving off boost the fueling was good.
We have replaced all the hoses connected to the carb, check the regulator pressure and changed needle (to a BDL). Nothing made a difference. So bottom line, we never got it tuned. Does anyone have any idea's on what will get rid of the lean out on boost?
The float level was check when we did the jet and is around 1mm. I noticed in the haynes manual that the later floats had a 2mm level. Could this be the problem?

Thanks for your help

’77 Clubman build thread
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Siamese 5 port EFI testing
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keeping lopping some off that needle.

regulator could be goosed and fuel pressure not rising with boost. same sypmtoms with a knackered pump that cant keep up or a kinked fuel line.

if the needle makes no difference then it has to be the supply.

That was our first thought so we checked the fuel pressure. It is rising on boost:
7psi boost, 10.5psi fuel pressure.
We also tried a BDK needle, all that did was mess up the tick over figures, but it still leaned out on boost.
As the enige is pretty much stock, we expected the fueling to work normally with stock parts.

’77 Clubman build thread
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=618189

Siamese 5 port EFI testing
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=611675

not always the case.

jimster uses a standard needle in his 160bhp + old engine

Tee-piece trick ???

No We have not tried the Tee-piece trick, obvious I guess. I remeber reading this before, when we had the initial probs back in the summer. I will give it a go tomorrow. Thanks For that.
One other quick question. I tried removing the balance pipe when we put the new jet in. The engine ran OK until we got back from a short 2 mile blip. There was oil smoke a plenty. We replaced the pipe and went for another run and the oil smoke disappeared. There has been no oil smoke since, so we have left the pipe in place. Any reason that this should have happened?

’77 Clubman build thread
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=618189

Siamese 5 port EFI testing
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=611675

Hi,
Correct gasket between carb and plenum?
Cheers,
Gavin :)

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As far as I know yes the gasket is correct. It does have the hole for the plenum feed to the carb. It was running fine until we took the carb off to change the jet (and I removed the balance pipe).

Incidentally the jet we took out was either very worn or was the wrong jet. There appears to be a significant difference in the size. Thinking maybe the previous owner of the Metro it came out of had the same problem and used a 0.125" jet to over come the lean out problem. I have not measure the old jet yet, but I say this because it has always run rich. It only just past the MOT on emissions. Just a thought, as the size difference is significant enough to notice by eye.

Going back to the Tee-piece trick: We put a gauge on the actuator signal output from the carb (the one 3/4" forward of the fuel input) and that was reading 6psi on boost. The boost gauge was reading 7psi,. Would that 1 psi difference be a problem?

’77 Clubman build thread
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=618189

Siamese 5 port EFI testing
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=611675

Hi,
Have you got the actuator connected to the carb?????
cheers,
Gavin :)

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No, the actuator signal output on the carb is blocked off.

’77 Clubman build thread
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=618189

Siamese 5 port EFI testing
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=611675

Hi,
You've lost me here what actuator signal on the carb?
Cheers,
Gavin :)

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Sorry, what I meant was the port from the carb, which is shown as item 4 on the picture from the thread below.
We have it blocked off, but tested the pressure here under boost. We got 6 PSI from here when the turbo was producing 7psi.
turbo.
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=2103.

’77 Clubman build thread
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=618189

Siamese 5 port EFI testing
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=611675

Hi,
Unless you was using the same guage for boost and the test on the carb, the 1psi difference could just be the gauge.
Try the tee piece trick and measure the pressure at point 4 again (tee the gauge in) to see if it's any higher, you may have a partial blockage in the carb.
Erm, just re reading above, what were the emissions readings for the MOT and did you try to adjust it? Also is the timing correct?
Cheers,
Gavin :)

Edited by Bat on 14th Apr, 2007.

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Hi,
Are you sure the jet you've got it there now is the right one?
Cheers,
Gavin :)

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well if you have plenty of fuel then all i can say is take it back and get him to lop some metal of the needle mate as this is more than litghly were the problem lies.

no teo engines are the same.

always looking for them bigger bunches of bannanas

Hi,
I'm concerned about the jet as the only 2 types I can find are 1 for the HIF38 and the other for HIF44.
As far as I can tell there's not a 0.125 jet to fit a HIF series carb.
Cheers,
Gavin :)

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There definately are 0.125 needle / jet combinations available.

Every day is a school day ...........

How fast and how expensive ...... the same question...

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Thanks for all your help everyone.
We tried the tee-piece trick which did not cure the problem.
We definately have 3.5psi above boost from the fuel pressure regulator.
I was wrong about the jet size. It is just a few thou above 0.100". There is a difference in OD on the brass insert between the new and old jet , which made the old jet look very big. The new jet is however slightly longer.
Avonbar have advised that the jet is correct. As the Mini is my dad's, He has spoken to Avonbar, who have advised him on what to do, I think replace the jet and up the fuel pressure to 4PSI above boost.
We have also adjusted the float setting and raised it to 1.5mm, the top tolerence on the haynes manual spec.
We are waiting for the new needle and I am looking for a wide band Lambda (as was origanally suggested to us in a previous thread) now we have some spare cash.
I do not know what the emission readings for the MOT were, but they did screw the carb right down and said that it was still very rich. The timing could possibly be out, but the RR operator would not touch it as he was concerned with the fuel mixture.
I will keep you posted to the outcome.
Thanks again

’77 Clubman build thread
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=618189

Siamese 5 port EFI testing
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=611675

sounds like you need a better RR operator...

I think you are right, but we can't find anyone in this area who knows much about 'A' series turbo's.
I guess making sure it all works before you go helps. The couple of people we have been to expect to just tweek a few things and get it running spot on.

’77 Clubman build thread
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=618189

Siamese 5 port EFI testing
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=611675

it does help but when you get stuck its the experts that are supposed to help.

I like my RR guy as he'll help me figure out whats wrong then say, right, take it away and fix it then bring it back

Hi,
I'm with Iain on this.
I'm confused that it was way rich on the MOT, you say it drives well but the RR says it's really weak.
Time for a second opinion?
Have you checked the float chamber pressure with the tee piece in place?
Cheers,
Gavin :)

Edited by Bat on 18th Apr, 2007.

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Which RR did you use? As you say cheltenham I am assuming that you visited Mech Repairs (www.rollingroad.co.uk), is that correct??

If so then you should have been in safe hands, they moan like hell about any carb that isn't a DCOE but they are actually VERY good with needle modifications. I have had all my Minis on their rollers and they have always done a very good job, my 122bhp 1380 runs far better than a carb'd dizzied engine ever should!!

I am not supprised that he wouldn't adjust the timing if it was set on the safe side and was leaning out as the last thing then need is your engine letting go on the rollers (believe me that is a pain in the ass!!!). A good RR guy should always aim to get the engine running safely before pushing for optomisation IMHO.

Next time you take the car there drop me a PM and I'll try to pop over and look through it with you, two heads better than one etc.

Every day is a school day ...........

How fast and how expensive ...... the same question...

Go see peter baldwin :)